Neighbor discovery is a process used by clients to discover neighboring clients and access points (APs) in a wireless local area network (WLAN). In a WLAN, typically the clients are endpoints of a communication path, and the APs are typically stationary and the intermediaries by which a communication path to a client may be established or maintained. It is generally desirable in a WLAN to have rapid establishment of communication links between clients and APs, and to have rapid handoff between APs, without errors and without inadvertently dropping the communication. This type of capability is generally accommodated by allowing the client to scan various channels where scan means to go from listening to a serving AP on one channel to listening to a neighboring AP on another channel. This allows the client to determine which AP or client to hand off to when the need to handoff occurs.
In general, IEEE 802.11 outlines two scanning methodologies to perform neighbor discovery. One is termed active scan and requires that clients broadcast a probe request packet which is heard by neighbors. Neighboring APs of the client respond by sending a probe response packet. Even though active scan allows a client to discover neighboring APs, active scan does not allow a client to determine neighboring clients, since clients do not send probe response packets. Thus, with active scan neighboring clients are hidden and not revealed during the process of neighbor discovery. Further, if a client constantly sends probe request packets because it has not received any probe response packets, and there are neighboring clients that are hidden from the client, then the superfluous probe request packets may cause unnecessary collisions or waste capacity in the wireless local area network.
The other scanning methodology is termed passive scan and requires a client to listen on a specific channel and determine its neighbors by decoding the packet transmissions on the channel. Even though passive scan allows a client to discover neighboring clients and APs, passive scan requires a client to spend much time listening to a channel. Spending an extended period of time listening to a channel may be a problem for clients which are small and have limited power and storage capabilities. Further, if neighboring clients are not sending packet transmissions, then a client that listens to a specific channel may not be able to determine neighboring clients. Thus, even with passive scan, neighboring clients may be hidden from the client. Further, scanning for long periods of time causes the clients to consume unnecessary power and strains the clients' limited storage capabilities.
The prior art methods of discovering neighbors has many limitations. Among them are that neighboring clients are not always revealed, unnecessary collisions are caused, capacity is wasted, and the amount of power of clients may be drained. Accordingly, there exists a need for an improved method of neighbor discovery in a wireless local area network.
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